This study evaluates the safety,three batches consistency and immunity duration of the
post-marketing inactivated Enterovirus Type 71 (EV71) vaccine in children aged 6-71
months.This study has two groups:safety observation group and immunogenicity observation
group.20000 subjects will receive 2 doses vaccines and be observed for safety among 2
epidemic cycles of HFMD.In the immunogenicity observation group, 900 subjects will be
randomly received 3 batches vaccines(2 doses),and blood sampled at days 0 and 56.